In recent years, due to the popularization of portable radio terminals, such as mobile cellular phones, portable information terminal machines, or the like, requests for trouble diagnosis and the like have greatly increased.
Accordingly, the conventional method, in which a faulty portable radio terminal is sent to the manufacturer to be diagnosed, is no longer satisfactory.
Therefore, in order to reduce the inconvenience to the user, a method involving fault diagnosis in shops, etc., is being used.
In this way, in order for testing of portable radio terminals to be carried out at the shops, etc. which are not electromagnetically shielded, an antenna coupler 10 as shown in FIG. 15 is used.
The antenna coupler 10 has a shield box 11 which is freely able to open and close for accommodating a portable radio terminal 1, which is a testing object, a coupling antenna 12, which is fixed in the shield box 11 and is spatially coupled to an antenna 1a of the portable radio terminal 1, and a terminal 13 which is attached to an external face portion of the shield box 11 and which is connected to the coupling antenna 12 in the shield box 11 to connect a coaxial cable 16 to the coupling antenna 12 in the shield box 11 from the exterior.
When testing of the portable radio terminal 1 is carried out by using such an antenna coupler 10, the shield box 11 is opened. The shield box 11 is closed after the portable radio terminal 1, which is the testing object, is set at a predetermined position in the shield box 11. The terminal 13 and a measuring device 15 are connected by the coaxial cable 16. Testing such as calling, incoming, and sensitivity, and the like of the portable radio terminal 1 is carried out by the measuring device 15.
As the coupling antenna 12 of the antenna coupler 10 to be used for such a purpose, there is the need to cover the frequency bandwidth allocated to the portable radio terminal 1 which is the testing object.
However, the frequency bandwidth of the portable radio terminal 1 is different for each system. For example, an 800 MHz or 1.5 GHz bandwidth order is used in a conventional method. On the other hand, a 2.2 GHz bandwidth order is used in the third-generation W-CDMA system whose operation has recently started.
Moreover, because tightness can be supposed even in each frequency bandwidth, allocation of the 5 GHz bandwidth order has been newly considered, and hereafter, measuring and testing for portable radio terminals over a wide frequency bandwidth will be required.
Therefore, in order for one antenna coupler 10 to be able to correspond to these portable radio terminals 1 whose systems are different, a wide frequency bandwidth characteristic of the coupling antenna 12 is required.
As a method for solving this problem, in the antenna coupler disclosed in U.S. Pat. No. 6,229,490, two antenna elements having different frequency ranges each other and coupled by a diplexer, are used.
Further, in this antenna coupler, by firmly securing the portable radio terminal which is the measuring object at a predetermined position with respect to these two antenna elements by a securing means, coupling attenuation between the portable radio terminal and the antenna elements is made to be constant, and measuring of receiving sensitivity and the like is carried out.
However, in a method in which two antenna elements having different frequency ranges each other and coupled by the diplexer as described above, in order to cover, for example, the 2.2 GHz bandwidth order allocated to third-generation portable radio terminals in addition to the 800 MHz bandwidth order and the 1.5 GHz bandwidth order allocated the current portable radio terminals as described above, antenna elements having further different frequency ranges each other are added, and these antenna elements must be coupled by the diplexer.
Therefore, in such an antenna coupler, since design of the coupled portion is not easy, and high manufacturing accuracy is required, there is the problem that the entire antenna coupler cannot be realized inexpensively.
Further, in the antenna coupler, the operation for firmly securing the portable radio terminal by the securing means is necessary. The operations are complicated, and the posture of the portable radio terminal is regulated by the securing means. Therefore, there is the problem that it cannot cope with all the various types of portable radio terminals whose shapes or antenna positions vary.